ES2788624T3 - Apparatus and method for monitoring hollow engineering structures - Google Patents

Abstract

Method for continuous monitoring of a civil engineering structure, the civil engineering structure comprising at least one hollow structural element comprising an internal closed compartment, in which the method is characterized by: - providing a pressure sensor, adapted to measure an internal fluid pressure in the internal closed compartment, - establishing an internal fluid pressure in the internal closed compartment, - providing a fluid connection between the at least one internal closed compartment and the pressure sensor, wherein providing a connection of fluid comprises connecting the pressure sensor directly with the internal closed compartment or arranging the pressure sensor inside the internal closed compartment, - providing a control unit that is configured to detect a change in the internal pressure value of the fluid, - monitor internal fluid pressure in order to detect a change in pressure internal fluid flow indicating a through-thickness crack in the internal closed compartment, in which continuous monitoring comprises monitoring for at least two weeks, and in which the pressure sensor compensates for changes in an ambient temperature and / or changes in ambient pressure and / or shock.

Description

DESCRIPTION

Apparatus and method for monitoring hollow engineering structures

The present invention relates to the monitoring of the structural state of civil engineering structures, especially to the continuous monitoring of structures, elements or hollow articles of such structures. It is based on the so-called Flooded Element Detection (FMD).

Civil engineering structures are normally subject to wear and tear, in particular periodic stress. A surface crack that typically occurs under fatigue loads in the case of hollow structures, as well as in the case of, for example, bridges, pedestrian overpasses, flyovers, piles, stadiums, towers, high ground structures Sea such as monopiles or tripiles, can become a crack through thickness (TTC). Growing TTCs can quickly cause additional damage and even destruction. Therefore, early detection and monitoring of cracks through thickness can help prevent damage and economic loss. In that case, by civil engineering structure, any artificial structure designed and / or built applying technical engineering skills and knowledge is taken into consideration. Examples of such structures include a treatment plant; a power plant; a tower; a cooling tower; a lock construction; any housing or industrial construction; a building construction; a cinema; a stadium; a pavilion; a bridge; a flyover; an overpass for pedestrians; an elevated lane; a ground connection thereof; an offshore shore connection of a wind generator or the like; a substation or wind turbine support; a scaffold; a scaffolding; a substructure; a basic work; a foundation; one base; a double bottom; a double hull; a pontoon or floating wind turbine support structure; a truss, eg flat chord truss; a support element or pile for any industrial equipment or platform.

Generally accepted non-destructive detection methods and techniques have been established for monitoring the structural condition of civil engineering structures. For example, in the natural gas and fuel industry, detection techniques based on x-rays and ultrasound are established. Thermographic methods are recognized and widespread in other areas of structural condition monitoring. However, each and every monitoring method cannot be used efficiently and economically directly in a different industry, for example, such as those currently booming, for example, in coastal regions and offshore. US 4 104906 A describes early crack detection with a multi-pressure system. Document US 2002/092855 A1 describes a self-monitoring method and an apparatus for monitoring the condition of a structure. Document FR 2384251 A1 describes a method and apparatus for the early detection of cracks in elements subject to significant limitations. WO 2009/065175 A1 describes a differential comparative pressure monitoring system. WO 2009/065174 A1 describes a comparative pressure monitoring instrument. Document EP 0415848 A1 describes a method for monitoring flexible tubular cables and pipes during operation and acoustic collection to implement this method. US 2012/099398 A1 describes a remote flooded element detection. Document US 2011/135468 A1 describes systems and methods for monitoring the structural state of a wind turbine.

In view of the above, a method for long-term monitoring of a hollow structure according to claim 1 is suggested, a method for maintaining a hollow structure according to claim 12 is suggested, the use of the method of claims 1- is suggested 11 according to claim 13, an apparatus for these methods according to claim 14 is suggested; and the use of the method according to claim 12 according to claim 21 is suggested. Additional embodiments, modifications and improvements appear from the following description, figures and claims.

According to one embodiment, a method for long-term monitoring of a civil engineering structure is suggested, wherein the civil engineering structure comprises at least one hollow element comprising an internal closed compartment. The suggested method comprises:

- establish an internal fluid pressure in the compartment;

- monitoring internal fluid pressure in order to detect a change in internal fluid pressure indicating a through-thickness crack in the compartment,

wherein the long-term monitoring comprises monitoring for at least two weeks, preferably for 1 month, more preferably for 1 year, especially for periods extending five years. In this case, establishing comprises passively measuring (ie detecting) a pressure that is present within the closed compartment. That pressure can be a fluid pressure produced, previously generated, or naturally occurring within the compartment. Alternatively, setting also comprises generating, ie actively producing, a given fluid pressure (a target pressure) which is taken as the starting pressure. By setting a certain threshold pressure value, deviations of a fluid pressure can be detected and actions can be taken, if the measured fluid pressure deviates more than the threshold value of the set fluid pressure.

Advantages of this method are, for example, its long-term applicability and its low costs, both for implementation as for maintenance and its applicability to a wide range of civil engineering structures as indicated above, for example, such as structures installed on land, a substation or wind turbine support; a scaffold, a scaffold, a substructure, a base work, a foundation, a base, a double bottom, a double hull, or a pontoon.

According to the further embodiment the method further comprises:

- provide a pressure sensor to measure the internal pressure of the fluid and whose signals are independent of ambient temperature and / or shock and

- providing a control unit that is configured to detect the change of the internal pressure value.

Advantages include robustness, reliability and anticipated failure detection even for a complex hollow structure, comprising multiple internal hollow compartments.

According to another embodiment, the pressure of a fluid inside the compartment is measured, wherein the fluid comprises a liquid or a gas, preferably a gas, such as air or a constituent element thereof.

The advantages are the easy accessibility of air and of the constituent elements of air, such as, for example, carbon dioxide, nitrogen, argon or others. In principle, any gas can be used to pressurize the hollow compartment. According to a modification, the hollow compartment, for example in a monopile-like structure, can be filled with water. The air pressure will simply be set above the water, while the hollow compartment will be filled primarily with water. Advantageously, the buoyancy of civil engineering structures such as monopiles or tripiles in an offshore region will be reduced and therefore the stability will be greatly improved.

According to another embodiment, the monitoring comprises:

- providing a fluid connection between the at least one compartment and the pressure sensor.

A fluid connection is required in order to establish an internal pressure value. Otherwise, the pressure cannot be measured.

According to an embodiment that provides a fluid connection, this comprises connecting the sensor directly with the internal hollow compartment or arranging the sensor inside said compartment.

Certain advantages include direct contact between the sensor and the fluid inside the compartment. No special precautions are required for the hermetic sealing of a connection between the sensor and the compartment since the sensor is placed directly into the fluid whose pressure is to be established.

According to one embodiment the step of "providing a fluid connection" comprises fluidly connecting the sensor by means of a tube, set of tubes, or capillary with respect to the hollow compartment. The tube, set of tubes, or capillary, as well as any coupling or fitting, ensures a fluid-tight and / or gas-tight connection between the sensor and the fluid within the compartment.

Advantageously, for reasons of ease of inspection, the sensor can be located at a distance from the compartment. Advantageously, the fittings and / or couplings are leak proof and have a design operating pressure higher than the fluid pressure in the hollow compartment.

According to another embodiment the method further comprises:

- provide clamping means for the tube or set of tubes.

The fastening of the tube, set of tubes or capillary for example to the walls of the hollow compartment allows the prevention of shocks and stable measurement values for long periods of time that only depend on the internal pressure.

According to one embodiment the fastening means are selected from a glue, a magnet, a coupling, a weld, or a clamp.

Advantageously such types of fasteners or their combination provide a reliable fixation for the tube, tube set or capillary. For example, a magnet adheres well to a steel or iron surface. Furthermore, the structural integrity of the monitored element is kept intact by a magnet, a glue-like adhesive, or a suitable spring or clamp and is hardly altered by coupling or welding. In addition, a length of tube or even multiple tube sections (tube bundle, capillary, tubing) can be reliably maintained if a fitting, flange, or manifold (for example, a manifold with multiple connections with connected tubes (tube bundle) tubes, capillaries, pipes) is fastened to the engineering structure or, for example, to the wall of its hollow internal compartment with the fastening means described above.

According to another embodiment the pressure sensor is selected from a pressure sensor such as piezoresistive, electromagnetic, optical, ionization-based, vibrating wire, an optical, piezoelectric, capacitive, thermal or potentiometer-based sensor.

Advantageously, the sensor is chosen from a wide range of sensors and can therefore be adapted to the special requirements of the special application, ie the special fluid or condition.

According to a modification of that embodiment, the pressure sensor compensates for changes in an ambient temperature and / or changes in an ambient pressure (eg, a fluctuation in daily ambient pressure) and / or a shock or vibration of the engineered structure. civil during its normal use.

Advantageously, the established pressure corresponds to a real pressure inside the hollow compartment.

According to another embodiment, the tube for fluid connection is selected from a polymeric or metal tube, preferably a polymeric tube. The tube can be selected, for example, from polyethylene, polyvinyl chloride, polypropylene, nitrile-based rubber, polyetheretherketone (PEEK), polyamide, ethylvinylacetate and other polymeric type tube assemblies, copper, aluminum or steel tube assemblies.

Advantages of polymeric capillary and tube assemblies include commercial availability, high reliability, resistance to corrosion (eg from salt water) and / or low price.

According to another embodiment, the generation of an internal target pressure comprises:

- providing compression means such as a gas pump, compressor or container comprising a pressurized gas and / or providing evacuation means such as an evacuation pump or a vacuum pump. The advantages of this embodiment include low maintenance costs and reliability. Especially, a gas container comprising pressurized gas equipped with, for example, a suitable needle valve does not require additional maintenance. Furthermore, advantageously, different types of pumps are commercially available.

According to another embodiment, the hollow structure comprises a hollow beam, a monopile, a cord that is welded to a clamp, and / or a clamp that is welded to a cord.

Advantageously, similar structures are quite common in civil engineering. The suggested monitoring method requires minimal maintenance costs, offers high reliability and robustness over long periods of use.

According to another embodiment, long-term monitoring comprises continuous monitoring for up to 50 years.

This allows easy monitoring at low costs between or even without additional periodic inspections.

According to another embodiment, a method of maintaining a hollow structure comprising at least one internal compartment is suggested, wherein the maintenance comprises:

- applying the method for long-term monitoring according to the embodiments described above;

detecting a pressure change in the at least one closed compartment indicating a leak, wherein the leak is selected from a crack through thickness or other opening,

- operating a pump in order to produce a jet of fluid, preferably a jet of gas, through the leak;

- locate the leak by determining the rise of gas bubbles and locate its starting point; Y

- close the leak.

Advantages include easy workability and low costs.

According to a further embodiment, it is suggested to use the described method for monitoring:

- a treatment plant; a power plant; a tower; a cooling tower; a lock construction; any housing or industrial construction; a building construction; a cinema; a stadium; a pavilion; a bridge; a flyover; an overpass for pedestrians; an elevated lane; or a ground connection thereof;

- an earthing structure, an offshore earthing connection of a wind generator; a substation or a wind turbine support; a scaffold; a scaffolding; a substructure; a basic work; a foundation; one base; a double bottom; a double hull; a pontoon or a floating wind turbine support structure; a truss; a truss of flat chords; a pile or support element for any industrial equipment or platform;

- an offshore monopile, a triplet, a support, a wind turbine support substructure, a wind turbine tower, an offshore transformer substation substructure.

According to yet another embodiment of the present invention, an apparatus for long-term monitoring of a civil engineering structure is suggested. The civil engineering structure comprises at least one closed internal compartment. The device comprises:

- a pressure sensor, adapted to measure an internal fluid pressure of the compartment;

- a controller for collecting and comparing the internal pressure with a set pressure or with a given threshold value, wherein the controller is adapted to detect a through-thickness crack in the compartment by detecting a change in the internal fluid pressure.

Advantages correspond to the advantages indicated above and comprise a good accessibility of the components necessary to configure said apparatus and the possibility of easily configuring such apparatus according to any given structure.

According to a further embodiment the apparatus further comprises:

- a warning device to indicate a through-thickness crack in the compartment.

Advantageously, any possible leakage, for example a through-thickness crack, can be easily detected, remarkably, even remotely from the monitored hollow structure.

According to another embodiment the apparatus further comprises:

- fastening means for fastening the tube or set of tubes to the hollow structure.

Such fastening means are selected in order to improve the functionality of a monitoring system comprising different pressure sensors that are fluidly connected to different internal hollow compartments. Furthermore, these fastening means can be applied easily and advantageously does not cause deterioration of the material structure or any element of the hollow structure.

According to another embodiment the civil engineering structure that is monitored by an apparatus as described above is selected from onshore or offshore engineering structures, in particular from: a wind turbine substation or support; a scaffold; a scaffolding; a substructure; a basic work; a foundation; a bridge; a tower; one base; a double bottom; a double hull; or a pontoon.

The advantages are low costs compared to high costs, required, for example, for specially trained personnel or a possible exposure of personnel or material to radioactivity, x-rays or ultrasonic energy as applied with known monitoring methods for offshore structures or expensive and complicated methods such as, for example, blocking thermography.

According to another embodiment, a separate sensor of the described apparatus is fluidly connected to at least two independent compartments.

Alternatively, according to yet another embodiment the at least two compartments are fluidly connected to each other and the sensor communicates fluidly with one of them, that is, the sensor is fluidly connected to one of them.

Advantageously the number of sensors can be reduced, although the reliability of the monitoring can be improved by a redundant design, i.e. redundant sensors.

According to another embodiment the apparatus described above further comprises fastening means for fastening the tube and / or set of tubes to the hollow structure, wherein the fastening is selected from fastening to the inside of and / or to the outside of the structure hollow, preferably, the fastening is selected from fastening to the interior of the hollow structure. The selected clamping advantages of clamping to the interior of the hollow structure comprise an improvement in the robustness of the entire system.

Furthermore, a through-thickness crack detection method is suggested for a grounding structure comprising at least one internal closed compartment. This comprises:

- establish an internal fluid pressure in the internal closed compartment;

- monitoring the internal fluid pressure for at least two weeks, preferably for 1 month, more preferably for 1 year, especially for periods extending five years;

detecting a change in the internal target pressure indicating a through-thickness crack in the at least one closed compartment.

Advantages are derived from the broad applicability of TTC detection methods in monitoring structural condition.

The attached figures illustrate different embodiments and together with the description serve for a further explanation and clarification of the principles of the present invention. Items in the figures are shown relative to one another and are not necessarily to scale. Identical designation numbers correspond to similar elements or parts in the drawings.

Figure 1 shows the growth at various stages of a crack through thickness from the point of view of flooded element detection (FMD);

Figure 2 shows an exemplary configuration of the monitoring system based on the method and apparatus described herein. Configuration refers to mechanical and electrical connections between elements of the system.

Figure 3 shows an embodiment with a grounding structure to be covered by a full version of the monitoring system described herein.

Figure 4 shows a K-clamp leg type connection cross-section drawing illustrating an embodiment of the present apparatus and method;

Figure 5 shows a laboratory scale installation as it is subjected to airtightness test; Figure 6 shows measurement data collected during laboratory scale system leak tests. Figure 7 shows an arrangement of air system valves and pressure sensors in the direction of pneumatic connections in the preferred embodiment;

Figure 8 shows the layout of the apparatus within the frame in a preferred embodiment.

Offshore operating conditions are considered harsh and severe. They can be dangerous for any type of structure built in a marine environment. These harsh environmental conditions can cause damage and structural failure. The causes of structural damage can be grouped into:

- failures resulting from statistical variations in loads and structural load bearing capacities;

- failures due to accidents;

- failures due to human error during the design, manufacture and / or operation of the structures.

Each of them can be detected by FMD techniques. The main direct causes of element flooding are:

- fatigue cracks through thickness;

- cracks originating from weld root defects;

- accidental damage; Y

- Anodic support failure causing corrosion.

A few decades ago there were serious fatigue problems related to offshore steel structures as most of the attention was paid to the static load bearing capacity. Therefore, historical records show that Fatigue Through Thickness Cracks (TTFC) are the most common offshore structural failure that can be detected by flooded element detection. The latest changes in the design approach introduced a special attention to fatigue design. An improvement in the structural capacity for cyclical loads was achieved, but it was never completely resolved in the sense of the entire useful life of the structure. These problems are the background for the Flooded Element Detection (FMD) technique and monitoring method described herein.

Flooded element detection is a well known inspection technique used to determine whether any element or clamp leg of an offshore substructure has:

- any crack through thickness;

- any corrosion through thickness; or

- any leak in the connection of non-welded structural elements.

FMD in some versions is a well known and developed inspection technique for items tubular. It has been used since the early 1980s.

It should be emphasized that the ultrasonic and gamma ray FMD techniques designed for the oil and gas industry are not suitable for direct transfer to new types of offshore structures and new ways of using them. There are also new versions of ultrasonic FMD in development, intended simply for offshore wind turbines. New approaches are described in [1] but have significant weaknesses that will be listed below in this document.

X-rays or gamma rays are the most commonly used media for FMD. However, certain significant disadvantages of this approach are:

- it is based on a radioactive medium, and therefore dangerous;

- requires the implementation of remotely operated vehicle (s) (some companies also offer diving equipment as an operator version);

- requires operators to be trained as radiation protection supervisors.

Ultrasonic FMD is an alternative method to the radioactive and unsafe approach described above. However, there are other significant disadvantages:

- tends to misalignment of the emitter probe

- requires removal of marine growth;

- time consuming due to the need for surface preparation.

Although there have been new versions of ultrasonic FMD developed simply for the offshore wind industry. Such are described, for example, in [1], but are still under development and:

- the useful life of the system depends on the service life of the battery,

- requires sophisticated ultrasonic receivers to correctly detect and normalize signals from sensors;

- Salt induced sensors can only be used once.

Although the apparatus and method described herein are based on conventional FMD that results from cracks through thickness, they overcome the stated disadvantages of these methods, for example, through early detection of damage, extremely low costs, and long-term reliability. term.

Figure 1 shows a typical K-joint of hollow section elements, that is, a tubular connection of two clamps to a cord. Different stages of crack propagation are shown from left to right along the indicated A-A section. While an initial crack in the curved region between the clamp and the bead remains undetected, the through-thickness crack shown in the middle will cause a pressure change at least inside the clamp and therefore may detected before a complete failure.

The main principle of the monitoring technique comprises the detection of an air flow by a pressure change that is caused by a crack through the thickness of a pressurized element. Figure 3 shows a typical structural element of a grounding structure, consisting of hollow elements, which are arranged between four tubular legs, for example two clamps 2a and 2b arranged between legs 1a and 1b. The clamps 2 and the legs 1 of a supporting support structure are usually dry on the inside and are airtight. They can present an overpressure up to a certain level. By having a pressure level higher than the water pressure at any depth (for example, for a water depth of 30 meters, a pressure higher than 4 bar) a crack through thickness will cause a clear detectable pressure drop. The principles are then described below based on an example of an offshore substation support. Therefore, a complete monitoring system includes all tubular structural components of the monitored structure, for example, such as those shown in Figure 3.

There are different options for device monitoring and processing with respect to compartment size and organization:

1) Compartments in relation to elements: Each structural element (for example, a clamp) will be connected with an air tube as shown in figure 4. This facilitates a location in relation to elements during monitoring. The exact location is done by detecting the air flow through the defect.

2) A compartment for each structural part: a structural part such as, for example, a clamp group will be connected with an air tube and is sealed off from any other element. The clamps of the clamp group are connected in an air-permeable manner with small drill holes. This facilitates a location with respect to structural part by means of the described monitoring apparatus and method. The exact location is done by detecting the air flow through the defect.

3) The whole structure is a single compartment: the whole structure is airtight, but the connections between the elements of the structure are permeable to air through small drilling holes. In this case, the location is entirely based on detecting airflow through the defect.

Depending on the given circumstances of a given structure, the described apparatus can be adapted to actual requirements. The adaptation comprises, for example, drilling holes that will connect the internal space of joined elements in the joint region during the production of supports.

Figure 4 shows a K-joint with a main cord 1 (leg) and two clamps 2, in which inside the leg air tubes 3 are held by means of the clamp 4, illustrating an embodiment of the apparatus and method present.

The monitoring apparatus and procedure indicates a crack through thickness and allows its repair using the redundancy of a support structure. By allowing a repair time this implies that a Leak Before Breaking (LBB) condition is met. It can be shown that for redundant structures such as supports there is an LBB (see eg [5]). After repair of the defect, the tender point behaves as a newly produced tender point or as a tender point with accumulated fatigue damage, but no crack (see, for example, [4]). The apparatus described herein is designed to provide a service life greater than or at least the design life of the support structure. This is achieved through a maximum reduction in the number of mechanical elements and the application of components with decades of proven performance, such as screw-type compressor; polymeric tubes; vibrating wire sensors; airtight system elements; ball valves; and neodymium magnets for air tube fasteners.

Advantageously, a screw type compressor has the ability to operate continuously for dozens of months with a typical "mean time between failures" (MTBF) greater than 40,000 hours, in particular with an MTBF value greater than 30,000 hours.

Advantageously, polymeric tubes (eg polyamide tubes) are resistant to wear and compressor oil and can be used at low temperatures.

Vibrating wire-type pressure sensors (see Box H in Figure 2) are remarkable devices with respect to durability, long-term sensor signal stability, and sensor life. There is a documented example [2] of a sensor test that lasted 27 years without any sensor failure. Furthermore, the pressure transducer as the second main component for pressure measurement has been in stable operation since 1984, which is until now for 29 years (see [3]).

Neodymium magnets are the strongest and most stable magnets known. They lose less than 1% of their strength over 10 years and the tube fasteners that are based on them are fatigue proof.

The proposed monitoring system provides information on any presence of TTC with better sensitivity than traditional FMD techniques. In contrast to traditional FMD techniques, the introduction of water by "flooding" is not required for the detection of a fault since the leakage of air from the overpressure element is sufficient. Since the viscosity of air is approximately 50 times less than the viscosity of water, the penetration of a TTC by air is much easier to detect when compared to water. Therefore, advantageously, TTC failure detection is much faster compared to conventional FMD. The presence of a TTC can be detected at two different levels. First, the monitoring system indicates which element has a TTC due to independent measurements of a pressure level for each of the monitored elements. Second, the exact point of a crack within a given element can be detected before and / or during the repair procedure. For element repair with a TTC overpressurization can be performed again by using the compressor (see box B in figure 2) and the appropriate air system valve (s) (see box C in figure 2). Air bubbles will be produced and the crack can be detected. Accurate TTC point detection is also possible above the water surface as changes in air pressure on the faulty element will generate an audible signal by flowing out of the air.

Advantageously, contrary to the monitoring method proposed in [1], the apparatus and method described in the present document can be used repeatedly. After a TTC occurs and after the repair action, the system can function as an unaffected element. It does not matter if the water is pumped out or stays in the compartment. Air can be pressurized again in the air system tubing assembly (see inset G in figure 2) connected in a branching manner to a certain compartment (see enlarged view in figure 4). A further advantage of the described monitoring principle is the applicability to each tubular element of a supporting structure, while requiring only minimal interference with a given structure. In In particular, the hole drilled from a leg to any clamp element connected to the leg may have a diameter of approximately 5 to 50 mm, particularly 10 to 25 mm, preferably 15 mm to 20 mm. Said connection represents the connection of pressurized compartments (see box E in figure 2) to the air tubing assembly system (see box D in figure 2).

The set of tubes (see box D in figure 2) that fluidly connects the pressure sensor (see box H in figure 2) to a given hollow structure (see box E in figure 2) can be installed advantageously inside the structure or an element and, therefore, protected against hostile environmental conditions. Furthermore, the use of neodymium magnets in combination with glue intended for magnets in most cases overcomes any need for additional adjustments, for example by welding.

The application of the suggested method does not require the attachment of any additional external equipment to the structure.

The ball valves (see box C in figure 2) that separate the tube bundle system (see box D in figure 2) from the compressor (see box B in figure 2) during pressure monitoring of the A typical internal compartment can be advantageously controlled remotely thanks to the ball valve actuators connected to the control, data acquisition and data transfer unit (see box A in figure 2).

Furthermore, the suggested monitoring device and method are independent of temperature fluctuation. An approach to eliminating temperature effects depends on the chosen version of the apparatus and the monitoring procedure and also depends on the required sensitivity of the system. For example, if the minimum required pressure change level to detect a TTC is accepted as 10% then the entire structure can act as a single compartment. Data normalization will only be based on the construction and operation principle of the pressure sensor used. The temperature sensor built into vibrating wire pressure sensors facilitates automatic sensor compensation and can also be used for pressure value normalization. This example is based on annual air and water temperature changes in North Sea water [6]. The second example concerns a high demand for TTC sensitivity. In this case, a suggested version of the monitoring apparatus and procedure will include independent pressure change monitoring within each single compartment of the support structure shown in Figure 3. Additionally, the temperature sensors (see box G in the Figure 2) can be deployed within the structure next to (see box G in Figure 8) or within the monitored compartments. In this version, the sensors collect information about the temperature inside the structure and allow the normalization of the pressure data in the event that a certain pressure sensor is distant from the monitored compartment and, therefore, at a different temperature. Compensation for the temperature dependence of the sensor will again be based on an integrated pressure sensor. This approach requires no more than 3% pressure change to detect a TTC in underwater elements. The declared activation level is again based on annual water temperature changes in the North Sea [6]. The flexibility in the approach to temperature compensation and data normalization is an advantage that allows the adjustment of the apparatus and method to a specific type of structure, monitoring requirements and available budget. Furthermore, the temperature sensors (see box G in figure 8) deployed on the legs (for example 1a and 1b in figure 3) next to certain compartments will be covered with sheets of polystyrene foam. Such a measure guarantees the insulation of the air inside the legs and allows a correct temperature measurement of the steel at a given sea depth.

However, airspeed and wave-induced vibrations and roll will affect the level of the TTC opening, once TTC has occurred. However, even the smallest TTC collected during experimental tests allows the detection of a pressure drop simply after tenths of a second.

In contrast to traditional FMD techniques, the present monitoring approach also does not depend on the depth of the sea in the range of typical support structure depth installations. Also, a weather window is not required to allow monitoring of tubular elements. In addition, the monitoring apparatus and method are independent of any marine growth, they do not require diving equipment or remotely operated vehicles. In particular, the monitoring is completely automatic.

In order to ensure data processing and storage in the event of a power failure, a battery will be used as part of the power supply unit (see box F in Figure 2). Therefore, a certain period of operation of the monitoring apparatus can be provided without external power supply. In the event of a power outage, the system switches to a safe emergency mode. In this state, the electronic circuitry of the signal transmission unit and / or the control unit (see box A in Figure 2) continues to collect and store information about any leaks. As an energy saving measure, the compressor (see box B in figure 2) will deactivate during power failure or power failure. The battery capacity is designed to facilitate unaffected system operation in the absence of an external power source.

The monitoring system as described complies with any relevant guideline regarding monitoring systems. monitoring and with regard to the evaluation of the structural condition, as well as with regard to the legal requirements of the Federal Maritime and Hydrographic Agency of Germany (BSH).

The monitoring system as described is designed to test itself on a regular basis. In contrast to the above, newer approaches to ultrasonic FMD described in [1] do not allow self-inspection. Different pressure levels within parts of the system will allow an automatic differentiation of the system failure from the occurrence of TTC. The pressure valves (see box C in figure 2), pressure sensors (see box H in figure 2) and the tubing assembly (see box D in figure 2) will be positioned, depending on the choice of apparatus and method chosen, on one, two, three or four corner legs of a support structure. The corner legs will pressurize at different pressure levels than the clamps. Any poor connection in the tube assemblies will lead to a pressure leveling between the leg and any clamps. Not only will it give information about the leak within the system, but it will also indicate which branch of the tube set has the fault.

Another embodiment of a self-testing capability is based on TTC simulation. The air system valves (see box C in Figure 2) shown in Figure 7 can be arranged such that each single compartment can be independently depressurized. It will be identical to the situation in which the TTC occurs. The reaction of the system will be observed in the test mode described and the performance of the system will be evaluated. This action will also test the compressor unit (see box B in figure 2) since all compartments require to be pressurized to default levels again.

According to detailed embodiments of the monitoring system and apparatus, the final output, that is, the information about the presence of a crack through thickness (TTC), will be transferred from the control, data acquisition and data transfer unit (see box A in Fig. 2) to, for example, a central information processing unit. In particular, to monitor basement structures in an offshore wind farm or facility, a system human-machine interface can be merged with a monitoring, control and data acquisition (SCADA) system of a wind farm.

SCADA systems used within offshore wind farms collect environmental data such as air speed and air direction; operating data such as the position of the wind turbine nacelle, rotor speed or pitch angle; Machinery status data such as main shaft vibration or gearbox oil temperature. Advantageously, thanks to such integration a SCADA system can now be expanded with information on structural performance, providing more detailed monitoring of wind assets. SCADA compatibility will further simplify data management since it can be integrated under a human-machine interface.

The normalized pressure for an exemplary monitoring period of 21 days is shown in Figure 6. The laboratory scale setup shown in Figure 5 has been leak tested. The absolute pressure values were normalized against the temperature pressure standard.

The test was carried out at an average ambient temperature of 22.7 ° C. The results were scaled for the 1 m3 volume clamp element in order to increase the sensitivity to leakage. According to estimates, the system will lose approximately 1% of the initial pressure in 1 year, which means that the impact of the leak on the operation of the system can be discriminated. Similar research was carried out with temperature variations from -20 ° C to 40 ° C. In this case, the average leak was found again in the same order as the ambient temperature.

In a preferred embodiment, the control, data acquisition and data transfer unit (see box A in figure 2) will be placed on top of the offshore substation as shown in figure 8 (see Box A in Figure 8). The main part of the unit discussed will be in the form of an industrial computer and auxiliary electronics. The unit will control the operation of the compressor and air system valves. It will collect information from pressure sensors, temperature sensors, and a compressor. The information will be sent to selected servers over a substation communication network. This network will also be used for remote system setup and configuration.

In a preferred embodiment, the air compressor and damper unit (see inset B in figure 2) will be positioned on top of the offshore substation as shown in figure 8 (see inset B in figure 8). The main part of the unit discussed will be in the form of a compressor and a buffer container.

In a preferred embodiment, the air system valve unit (see box C in figure 2) will be integrated with the pressure sensor unit (see box H in figure 2) which will be placed in a housing in the Inside the upper part of the offshore substation legs. There will be a separate housing for each leg as shown in figure 8 (see inset C and inset H in figure 8). The main content of the commented casing will present the form of valves and pressure sensors, one pair for each hollow element as shown in figure 7.

In a preferred embodiment, the air system tubing assembly unit (see box D in Figure 2) will consist of 8 main branches collected into 2 groups. In a first group are the ramifications located inside each leg and in a second group are the branches in the path from each leg to the compressor unit. These groups are shown in figure 8 (see boxes D in figure 8). The main part of the unit discussed will feature the shape of polyamide tubes and air system fittings intended for offshore use.

In a preferred embodiment, the pressurized compartments (see inset E in Figure 2) are in the form of bracket elements according to structural corner and split legs. Exemplary compartments are shown in Figure 8 (see Box E in Figure 8).

In a preferred embodiment, a power supply unit (see box F in figure 2) will be placed on top of the offshore substation as shown in figure 8 (see box F in figure 8 ). The main part of the discussed unit will be in the form of electrical converter supply power from an external source for typical system operation and a battery to be used in an emergency mode as previously described herein.

In a preferred embodiment, the temperature sensor unit (see inset G in Figure 2) will consist of separate temperature sensors positioned at leg clamp convergence locations. Exemplary convergence locations within a leg are shown in Figure 8 (see inset G in Figure 8). The temperature sensors will be connected in series and additionally with the control unit (see box A in figure 2).

Summarizing the above, it is hereby suggested:

A method for long-term monitoring of a civil engineering structure, the civil engineering structure comprising at least one hollow element comprising an internal closed compartment, the method comprising:

establishing an internal fluid pressure in the compartment;

monitoring internal fluid pressure in order to detect a change in internal fluid pressure indicating a through-thickness crack in the compartment, wherein long-term monitoring comprises monitoring for at least two weeks, preferably for 1 month, more preferably for 1 year, especially for periods extending five years;

use said method for monitoring: a treatment plant; a power plant; a tower; a cooling tower; a lock construction; any housing or industrial construction; a building construction; a cinema; a stadium; a pavilion; a bridge; a flyover; an overpass for pedestrians; an elevated lane; or a ground connection thereof; a grounding structure, an offshore grounding of a wind generator; a substation or a wind turbine support; a scaffold; a scaffolding; a substructure; a basic work; a foundation; one base; a double bottom; a double hull; a pontoon or a floating wind turbine support structure; a truss; a truss of flat chords; a pile or support element for any industrial equipment or platform; an offshore monopile, a triplet, a bracket, a wind turbine support substructure, a wind turbine tower, an offshore transformer substation substructure;

an apparatus for long-term monitoring of a civil engineering structure comprising a hollow structure, the hollow structure comprising at least one closed internal compartment, the apparatus comprising: a pressure sensor, adapted to measure an internal pressure of fluid in the compartment;

a controller for collecting and comparing the internal pressure with a set pressure or with a given threshold value, the controller being adapted to detect a through thickness crack in the compartment by a change in the internal fluid pressure; Y

a TTC detection method for a grounding structure comprising at least one internal closed compartment, the TTC detection method comprising:

establishing an internal fluid pressure in the internal closed compartment;

monitoring internal fluid pressure for at least two weeks, preferably for 1 month, more preferably for 1 year, especially for periods extending five years;

detecting a change in internal target pressure indicating a through-thickness crack in the at least one closed compartment.

References

[1] Mijarez R., Gaydecki P., Burdekin M. (2007). “Flood element detection for real-time structural health monitoring of sub-sea structures of offshore steel oilrigs”. Smart Materials and Structures 16 (2007): 1857-1869;

[2] DiBiagio E. (2003). “A case study of vibrating-wire sensors that have vibrated continuously for 27 years”. Norwegian Geotechnical Institute. 6th International Symposium on Field Measurements in Geomechanics; Field measurements in geomechanics. ISBN: 9058096025;

[3] Geokon Inc., "Long-Term Stability Data for Geokon Pressure Transducers";

[4] Straub, D. (2004). "Generic Approaches to Risk Based Inspection Planning for Steel Structures." IBK Bericht 284. Zurich, ETH Zurich;

[5] Kou, K. P. and F. M. Burdekin (2008). "The applicability of leak-before-break on flooded element detection for offshore structures under fatigue." Engineering Fracture Mechanics 75 (1): 31-40;

[6] Korevaar, C. G. (1989). "Climatological data for the North Sea based on observations by voluntary observing ships over the period 1961-1980". Royal Meteorological Institute of the Netherlands.

Claims (21)

1. Method for continuous monitoring of a civil engineering structure, the civil engineering structure comprising at least one hollow structural element comprising an internal closed compartment, wherein the method is characterized by: - provide a pressure sensor, adapted to measure an internal pressure of fluid in the internal closed compartment, - establish an internal fluid pressure in the internal closed compartment, - providing a fluid connection between the at least one internal closed compartment and the pressure sensor, wherein providing a fluid connection comprises connecting the pressure sensor directly with the internal closed compartment or arranging the pressure sensor inside the internal closed compartment, - providing a control unit that is configured to detect a change in the internal fluid pressure value, - monitor the internal fluid pressure in order to detect a change in the internal fluid pressure indicating a through-thickness crack in the internal closed compartment, wherein continuous monitoring comprises monitoring for at least two weeks, and wherein the pressure sensor compensates for changes in an ambient temperature and / or changes in an ambient pressure and / or a shock. A method according to claim 1, wherein a fluid within the internal closed compartment comprises a liquid or a gas. A method according to claim 2, in which the gas is air or a constituent element thereof. A method according to claim 1, wherein providing a fluid connection comprises connecting the sensor to the internal closed compartment by means of a tube, tubing, tubing, or capillary. 5. The method of claim 4, further comprising: - provide clamping means for the tube or set of tubes. 6. Method according to claim 5, wherein the fastening means is selected from a glue, a magnet, a coupling, a weld or a clamp. Method according to one of the preceding claims, in which the pressure sensor is selected from a pressure sensor such as a piezoresistive, electromagnetic, optical, ionization-based, vibrating wire, optical, piezoelectric, capacitive, thermal or based on potentiometer. A method according to any one of claims 4 to 6, wherein the tube, tubing assembly, capillary or tubing comprises polyethylene, polyvinyl chloride, polypropylene, nitrile-based rubber, polyetheretherketone (PEEK), polyamide, ethylvinyl acetate or any another polymer, copper, aluminum, or steel. Method according to one of the preceding claims, wherein generating an internal fluid pressure comprises: - providing a gas pump or container comprising a pressurized gas, and / or - provide means of evacuation such as an evacuation pump or a vacuum pump. Method according to one of the preceding claims, in which the hollow structural element comprises a hollow beam, a monopile, and / or a clamp that is welded to a cord or a cord that is welded to a clamp. Method according to one of the preceding claims, wherein the continuous monitoring comprises monitoring up to 50 years. 12. Method for maintaining a hollow structural element comprising at least one internal closed compartment characterized by: - applying the method for continuous monitoring according to claims 1 to 11; detecting a pressure change in the at least one internal closed compartment, indicating a leak, selected from a through-thickness crack or other opening; - operating a pump in order to produce a jet of fluid, preferably a jet of gas, through the leak; - locate the leak; - repair the leak. 13. Use of the method according to any of claims 1 to 11, for monitoring: - a treatment plant; a power plant; a tower; a cooling tower; a lock construction; any housing or industrial construction; a building construction; a cinema; a stadium; a pavilion; a bridge; a flyover; an overpass for pedestrians; an elevated lane; or a ground connection thereof; - an earthing structure, an offshore earthing connection of a wind generator; a substation or a wind turbine support; a scaffold; a scaffolding; a substructure; a basic work; a foundation; one base; a double bottom; a double hull; a pontoon or a floating wind turbine support structure; a truss; a flat chord truss; a pile or support element for any industrial equipment or platform; - an offshore monopile, a triplet, a support, a wind turbine support substructure, a wind turbine tower, an offshore transformer substation substructure. 14. Apparatus for continuous monitoring of a civil engineering structure comprising a hollow structural element, the hollow structural element comprising at least one closed internal compartment, characterized by: - a pressure sensor, adapted to measure an internal pressure of fluid in the at least one closed internal compartment, in which the pressure sensor is either directly connected to the internal closed compartment or arranged within the closed compartment, and in which the pressure sensor is configured to compensate for changes in a ambient temperature and / or changes in ambient pressure and / or shock; - a fluid connection between the at least one internal closed compartment and the pressure sensor; - a controller for collecting and comparing the internal pressure with a set pressure or with a given threshold value, the controller being adapted to detect a through-thickness crack in the at least one closed internal compartment by a change of the internal fluid pressure , wherein the continuous monitoring comprises monitoring for at least two weeks. 15. Apparatus according to claim 14, further comprising: - a warning device for indicating a through-thickness crack in the at least one internal closed compartment. 16. Apparatus according to claim 14 or 15, further comprising: - fastening means for fastening the tube or set of tubes to the hollow structural element. Apparatus according to claims 14 to 16, wherein the civil engineering structure is selected from land or coastal and offshore engineering structures, in particular from: a wind turbine substation or support; a scaffold, a scaffold, a substructure, a base work, a foundation, a base, a double bottom, a double hull, a pontoon or floating wind turbine support structure, a bridge or a tower. Apparatus according to one of claims 14 to 17, wherein a sensor is fluidly connected to at least two independent internal closed compartments. Apparatus according to claim 18, wherein the at least two internal closed compartments are fluidly connected to each other and the sensor communicates fluidly with one of them. 20. Apparatus according to claims 14 to 19, further comprising fastening means for fastening the tube and / or set of tubes to the hollow structural element, wherein the fastening is selected from fastening to the interior of and / or to the exterior of the hollow structural element. 21. Use of the method according to claim 12 for the detection of cracks through thickness in an earthing structure comprising the at least one hollow structural element, characterized by: - establish an internal fluid pressure in the internal closed compartment; - monitor internal fluid pressure for at least two weeks; detecting a change in internal fluid pressure indicating a through-thickness crack in the internal closed compartment.